Semiconductor light-emitting device capable of having good stability in fundamental mode of oscillation, decreasing current leakage, and lowering oscillation threshold limit, and method of making the same

ABSTRACT

A semiconductor laser device includes a substrate having one of p- and n-conductivity types, and a current constrictive layer formed on a surface of the substrate and having the other type of conductivity. The current constrictive layer has a through-channel extending to the surface of the substrate for defining a current path in a direction perpendicular to the surface of the substrate. The through-channel is of a belt-like pattern extending in a direction perpendicular to end surfaces of the substrate. A third cladding layer having the one type of conductivity is filled in the through-channel, a surface of the third cladding layer being flush with a surface of a current constrictive layer. A first cladding layer, an active layer, and a second cladding layer which constitute a double heterostructure are formed over the third cladding layer and current constrictive layer.

This application is a division of application Ser. No. 08/253,363 filedJun. 3, 1994.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to semiconductor light-emitting devicesand methods for making such devices. More particularly, the inventionrelates to a short wavelength semiconductor laser which emits lightbeams of red to orange colors and a light emitting diode (LED) having awavelength band of red to green colors, and methods for making the same.

2. Description of the Prior Art

Recently, red semiconductor lasers having a wavelength band of 630 to680 nm constructed of AlGaInP have been receiving attention as apromising source of light for POS, as well as for high definition, highdensity photomagnetic disks. Indeed, researches and developments havebeen made in this connection. When such laser is used for disks,fundamental mode stability and good optical characteristics such asastigmatism and so on, in particular are important. For this reason,there exists a need for a semiconductor laser of the refractive indexguide type which confines light beams within the region of oscillation.

Refractive index guide type semiconductor laser devices of 680 nmwavelength band have hitherto been known including one shown in FIG. 11which is of the effective refractive index guide type, and another shownin FIG. 12 which is of the real refractive index guide type. FIG. 11 isa sectional view showing the semiconductor laser device of the effectiverefractive index guide type, and FIG. 12 is a sectional view showing thesemiconductor laser device of the real refractive index guide type. Thesemiconductor laser device shown in FIG. 11 is fabricated in such a waythat on an n-GaAs substrate 131 having (100) face as a main face aregrown an n-(Al₀.5 Ga₀.5)₀.5 In₀.5 P cladding layer (1.5 μm thick) 133, anon-doped Ga₀.5 In₀.5 P active layer (0.05 μm thick) 134, a p-(Al₀.5Ga₀.5)₀.5 In₀.5 P cladding layer (1.5 μm thick) 135, and a p-Ga₀.5 In₀.5P intermediate layer 136 according to a MOCVD (Metal Organic ChemicalVapor Deposition) process. Then, the intermediate layer 136 and an upperportion of the cladding layer 135 are removed by etching, leaving acentrally located ridge portion 141. Subsequently, n-GaAs currentconstrictive layers 132 are grown on both sides of the ridge portion 141and, in addition, a p-GaAs contact layer 137 (2 μm thick) is grown overthe entire region. Finally, electrodes 139, 140 are formed respectivelyon the underside of the substrate 131 and on the surface of the contactlayer 137. In such a semiconductor laser, the current constrictivelayers 132 limit current passage to decrease ineffective current andcause a substantially large mode loss relative to a higher order mode ofoscillation. Thus, an oscillation mode of higher order is suppressed sothat oscillation of the fundamental mode is steadily maintained inoscillation region 134a to a high light output.

The semiconductor laser device shown in FIG. 12 is fabricated in such away that on a p-GaAs substrate 101 having (100) face is formed an n-GaAscurrent constrictive layer 102 in which a channel 102b is formedreaching from the surface of the layer 102 into the substrate 101. Then,a p-(Al₀.5 Ga₀.5)₀.5 In₀.5 P cladding layer (1.8 μm thick) 103, anon-doped Ga₀.5 In₀.5 P active layer (0.05 μm) 104, an n-(Al₀.5Ga₀.5)₀.5 In₀.5 P cladding layer (1.5 μm thick) 105, and an n-Ga₀.5In₀.5 P contact layer (1 μm thick) 106 are sequentially formed over thelayer 102 according to the MOCVD process (where each layer thicknessvalue denotes the thickness of the respective layer in the channel).Finally, electrodes 109, 110 are formed respectively on the underside ofthe substrate 101 and on the surface of the contact layer 106. In thestage of growth according to the MOCVD process, the layer being grownusually reflects the configuration of the base layer. Therefore, theactive layer 104 is of such a configuration that it is largely bentabove the edge of the channel 102b, that is, above corresponding ends ofthe current constrictive layer 102, whereby a real refractive indexguide structure is formed. According to this arrangement, possible lossin the fundamental mode is reduced, which results in reduced thresholdoscillation value and increased differential efficiency.

Unfortunately, however, the semiconductor layer shown in FIG. 1 involvesa problem that the stability of the fundamental mode depends largely onthe thickness (residual thickness) d of the cladding layer portionsremaining at both sides of the ridge 141. This means that when etchingvariations are so wide that the residual thickness d substantiallyexceeds 0.3 μm, the fundamental mode is rendered unstable. (It is notedin this connection that an optimum value of residual thickness d isapproximately 0.2 μm.) The same is true with the case in which residualthickness d differs on opposite sides of the ridge 141. Another problemis that in the stage of current constrictive layer 132 growing, the baselayer for such growth is a layer including Al, that is, the p-(Al₀.5Ga₀.5)₀.5 In₀.5 P layer 135, which fact is likely to be a cause ofoxidation so that the quality of a regrown interface 135a will beunfavorably affected. This results in current leaks which in turn leadto an increase in the oscillation threshold value. Typically, anon-coated device having a resonator length of 400 μm has an oscillationthreshold value of 45 mA and a kink level of about 25 mW.

The semiconductor laser device shown in FIG. 12, wherein the activelayer 104 is largely bent at ends of the current constrictive layer 102to provide a real refractive index guide construction, has smallerlosses in both fundamental and higher order modes. This presents aproblem that the kink level becomes rather lowered. Typically, anon-coated device having a resonator length of 400 μm has an oscillationthreshold value of 25 to 30 mA and a kink level of about 20 mW.

SUMMARY OF THE INVENTION

The object of the present invention is therefore to provide asemiconductor light-emitting device having a current constrictive layerwhich has improved performance characteristics, and a method of makingthe same. Semiconductor light-emitting devices to which the invention isdirected include, in particular, semiconductor laser devices andlight-emitting diodes.

In order to achieve the aforementioned object, there is provided asemiconductor light-emitting device including a substrate having one ofp- and n- conductivity types, a current constrictive layer formed on asurface of the substrate and having the other of the p- and n-conductivity types, the current constrictive layer having at least onethrough-channel extending to the surface of the substrate for defining acurrent path in a direction perpendicular to the surface of thesubstrate, and a double heterostructure formed on the currentconstrictive layer and including a first cladding layer, an active layerand a second cladding layer, characterized in that:

the through-channel is of a belt-like pattern which extendsperpendicularly to end surfaces of the substrate; and the semiconductorlight-emitting device comprises

a third cladding layer having the one type of conductivity, at least oneportion of the third cladding layer being filled in the through-channel,and the at least one portion of the third cladding layer having asurface flush with a surface of the current constrictive layer.

The semiconductor light emitting device includes the currentconstrictive layer formed on the surface of the substrate having one ofthe p- and n- conductivity types, the current constrictive layer havingthe other of the p- and n- conductivity types. The current constrictivelayer has the through-channel of a belt-like pattern extendingperpendicularly to the end surfaces of the substrate. Therefore, thissemiconductor light-emitting device can constitute a refractive indexguide type semiconductor laser device. The semiconductor laser devicehas the third cladding layer of the one conductivity type filled in thethrough-channel of the current constrictive layer, the surface of thethird cladding layer being flush with the surface of the currentconstrictive layer. A first cladding layer, an active layer and a secondcladding layer which constitute a double heterostructure are formed by aknown growth method, for example, MOCVD process, flatly over the currentconstrictive and third cladding layers in a well-controlled manner,without involving any stage of etching. Therefore, the first claddinglayer, active layer and second cladding layer involve almost novariation in thickness. This insures good stability in the fundamentalmode of laser oscillation. The fact that no etching stage is involvedafter the formation of the third cladding layer eliminates thepossibility of any growth interface being oxidized. This results indecreased current leakage and lowered oscillation threshold limit. Thefirst cladding layer is usually designed to be relatively thin and in nocase does this result in decreased higher-order mode loss. Therefore,good improvement is achieved in kink level. In this way, thesemiconductor laser device having improved performance characteristicscan be obtained.

According to an embodiment, the third cladding layer has an extendedportion covering the surface of the current constrictive layer, theextended portion having a thickness set thinner than that of the portionof the third cladding layer filled in the through-channel.

According to the above arrangement, the third cladding layer has theextended portion covering the surface of the current constrictive layer,and the extended portion has a thickness set thinner than that of theportion filled in the through-channel. In this case, when the layerswhich make a double heterostructure are formed using, for example, theMOCVD process, the active layer becomes slightly bent adjacent edge ofthe through-channel. As a result, a waveguide arrangement is obtainedwhich has both a characteristic of an effective refractive index guidestructure utilizing the light absorption of the substrate (currentconstrictive layer) and a characteristic of a real refractive indexguide structure utilizing a bend of the active layer, that is, theadvantages of both of the prior art arrangements described. In otherwords, the semiconductor laser device can reduce mode loss relative tothe fundamental mode and increase mode loss relative to the higher-ordermode, so that the fundamental mode is further stabilized.

A semiconductor light-emitting device of an embodiment comprisesextension to the current constrictive layer having the other type ofconductivity and filled in a peripheral portion of the through-channel,the extension having a surface flush with the surface of the currentconstrictive layer; and

the third cladding layer being disposed inward of the extension to thecurrent constrictive layer within the through-channel.

With the above arrangement, the extension to the current constrictivelayer which has the other type of conductivity is filled in theperipheral portion of the through-channel, and the surface of theextension is flush with the surface of the current constrictive layer.Further, the third cladding layer is filled inward of the extension tothe current constrictive layer within the through-channel. Therefore, inoperation a width of current injection is proportionally reduced by theextension to the current constrictive layer. Therefore, an oscillationthreshold value thereof is further reduced and, in addition, someastigmatism reduction is achieved.

According to an embodiment, a plurality of the through-channels areformed in the current constrictive layer, the third cladding layer beingembedded in each of the through-channels.

With the above arrangement, the plurality of through-channels are formedin the current constrictive layer, with the third cladding layer beingembedded in each of the through-channels. Thus, in operation a pluralityof oscillation regions develop according to the number of current pathsformed by the through-channels. This provides a semiconductor laserarray.

A semiconductor light-emitting device of an embodiment comprises atleast one non-through channel formed in parallel with thethrough-channel in the current constrictive layer to a depth not greaterthan the depth of the current constrictive layer; and

a fourth cladding layer having the one type of conductivity and filledin the non-through channel, the fourth cladding layer having a surfaceflush with the surface of the current constrictive layer.

According to the arrangement, the at least one non-through channel isformed in parallel with the through-channel in the current constrictivelayer to a depth not greater than the depth of the current constrictivelayer, and further a fourth cladding layer having the one type ofconductivity is filled in the non-through channel, the surface of thefourth cladding layer being flush with the surface of the currentconstrictive layer. In this case, any strain that is applied to theactive layer because of the respective layers stacked on the substrateis dispersed over the non-through channel. Thus, the strain exerted onthe oscillation region over the through-channel is alleviated so that along-term reliability of the device can be enhanced.

Also, there is provided a semiconductor light-emitting device includinga substrate having one of p- and n- conductivity types, a currentconstrictive layer formed on a surface of the substrate and having theother of the p- and n- conductivity types, the current constrictivelayer having a through-channel extending to the surface of the substratefor defining a current path in a direction perpendicular to the surfaceof the substrate, and a double heterostructure formed on the currentconstrictive layer and including a first cladding layer, an active layerand a second cladding layer, characterized in that:

the through-channel is of a circular pattern; and the semiconductorlight-emitting device comprises

a third cladding layer having the one type of conductivity and filled inthe through-channel, the third cladding layer having a surface flushwith the surface of the current constrictive layer.

The semiconductor light-emitting device includes the substrate havingone of the p- and n- conductivity types, and the current constrictivelayer formed on the surface of the substrate and having the other of thep- and n- conductivity types, the current constrictive layer having thethrough-channel of a circular pattern formed therein. Accordingly, thissemiconductor light-emitting device can constitute a surface output typelight-emitting diode. The light-emitting diode comprises the thirdcladding layer having the one type of conductivity and filled in thethrough-channel, the third cladding layer having a surface flush withthe surface of the current constrictive layer. Therefore, the firstcladding layer, active layer and second cladding layer which constitutethe double heterostructure are formed by a known growth method, forexample, MOCVD process, flatly over the current constrictive and thirdcladding layers in a well-controlled manner, without involving any stageof etching. Therefore, the first cladding layer, active layer and secondcladding layer involve almost no variation in thickness. This insuresgood stability in radiation intensity--applied current characteristics.The fact that no etching stage is involved after the formation of thethird cladding layer eliminates the possibility of any growth interfacebeing oxidized. This results in decreased current leakage and increasedlight emission intensity. In this way, the light-emitting diode havingimproved performance characteristics can be obtained.

Where the layer forming the double heterostructure is configured to befrusto-conical, the efficiency of light output of the device can beenhanced.

According to an embodiment, the substrate is a GaAs substrate, thesurface of the substrate being (111)B face or a face offset to the(111)B face which is a main face;

the current constrictive layer is comprised of GaAs or AlGaAs; and

the third cladding layer is comprised of AlGaAs.

According to the arrangement, the substrate is the GaAs substrate havingthe (111)B face or the face offset to the (111)B face which is a mainface; the current constrictive layer is comprised of GaAs or AlGaAs; andthe third cladding layer is comprised of AlGaAs. In this case, as willbe described hereinafter, it is possible to grow the third claddinglayer comprised of AlGaAs having the one type of conductivity within thethrough-channel while the substrate is kept at a temperature of not morethan 720° C. in such a manner that the surface of the third claddinglayer becomes flush with the surface of the current constrictive layerthereby to fill the through-channel. Therefore, the first claddinglayer, active layer, and second cladding layer which constitute a doubleheterostructure can be grown by the known growth technique flatly overthe substrate in a well controlled manner.

There is provided a method of making a semiconductor light-emittingdevice comprising the steps of:

forming on a surface of a GaAs substrate having one of p- andn-conductivity types a current constrictive layer comprised of GaAs orAlGaAs and having the other of the p- and n-conductivity types, thesurface being (111)B face or a face offset to the (111)B face which is amain face;

forming in the current constrictive layer a through-channel of apredetermined pattern which extends from a surface of the currentconstrictive layer to the substrate;

growing a third cladding layer comprised of AlGaAs and having the onetype of conductivity within the through-channel while the substrate iskept at a temperature of not more than 720° C. to fill thethrough-channel with the third cladding layer in such a manner that thesurface of the third cladding layer becomes flush with the surface ofthe current constrictive layer; and

successively growing a first cladding layer, an active layer, and asecond cladding layer over the substrate to form a doubleheterostructure.

According to the method of making a semiconductor light-emitting device,on the surface of the GaAs substrate having the one of the p- andn-conductivity types is formed the current constrictive layer comprisedof GaAs or AlGaAs and having the other of the p- and n-conductivitytypes, the substrate surface having (111)B face or a face offset to the(111)B face which is a main face. The through-channel of thepredetermined pattern which extends from the surface of the currentconstrictive layer to the substrate is then formed in the currentconstrictive layer. Then, the third cladding layer comprised of AlGaAsand having the one type of conductivity is grown within thethrough-channel while the substrate is kept at the temperature of notmore than 720° C. This enables the third cladding layer to be grown sothat its surface becomes flush with the surface of the currentconstrictive layer thereby to fill the through-channel. Therefore, thefirst cladding layer, active layer, and second cladding layer can beformed flatly over the third cladding layer and current constrictivelayer in a well controlled manner to form a double heterostructure.Thus, it is now possible to fabricate semiconductor light-emittingdevices, such as a semiconductor laser device and a light-emittingdiode, which have good characteristic improvement over the prior artdevices.

Also, there is provided a method of making a semiconductorlight-emitting device comprising the steps of:

forming on a surface of a GaAs substrate having one of p- andn-conductivity types a current constrictive layer comprised of GaAs orAlGaAs and having the other of the p- and n-conductivity types, thesurface being (111)B face or a face offset to the (111)B face which is amain face;

forming in the current constrictive layer a through-channel of apredetermined pattern which extends from a surface of the currentconstrictive layer to the substrate;

growing a third cladding layer comprised of AlGaAs and having the onetype of conductivity while the substrate is kept within a temperaturerange of 720° C. to 740° C. in such a manner that one portion of thethird cladding layer which fills the through-channel has a surface flushwith the surface of the current constrictive layer and that the thirdcladding layer has an extended portion overlying the surface of thecurrent constrictive layer and being thinner than the fill portion; and

successively growing a first cladding layer, an active layer, and asecond cladding layer over the substrate to form a doubleheterostructure.

According to the method of making a semiconductor light-emitting device,after the through-channel is formed in the current constrictive layer,the third cladding layer comprised of AlGaAs and having the one type ofconductivity is grown while the substrate is kept within the temperaturerange of 720° C. to 740° C. so as to fill the through-channel in such amanner that the surface of that portion of the third cladding layerwhich fills the through-channel is flush with the surface of the currentconstrictive layer and that the third cladding layer has an extendedportion overlying the surface of the current constrictive layer which isthinner than the fill portion. Therefore, when the layers constitutingthe double heterostructure are formed on the current constrictive layerusing, for example, the MOCVD technique, the active layer is configuredto be slightly bent adjacent the edge of the through-channel. As aresult, the semiconductor light-emitting device made has a waveguidearrangement featuring both the characteristic of an effective refractiveindex guide structure utilizing the light absorption of the substrate(current constrictive layer) and the characteristic of a real refractiveindex guide structure utilizing the bend of the active layer, that is,the advantages of both of the prior art arrangements shown. In otherwords, the semiconductor laser device can reduce mode loss relative tothe fundamental mode and increase mode loss relative to the higher-ordermode, so that the fundamental mode is further stabilized. Furthermore,possible current leaks are reduced and the oscillation threshold limitis lowered.

Also, there is provided a method of making a semiconductorlight-emitting device comprising the steps of:

forming on a surface of a GaAs substrate having one of p- andn-conductivity types a current constrictive layer comprised of GaAs orAlGaAs and having the other of the p- and n-conductivity types, thesurface being (111)B face or a face offset to the (111)B face which is amain face;

forming in the current constrictive layer a through-channel of apredetermined pattern which extends from a surface of the currentconstrictive layer to the substrate;

growing in a peripheral portion of the through-channel an extension tothe current constrictive layer which is comprised of GaAs or AlGaAs andhas the other type of conductivity while the substrate is kept at atemperature of not more than 720° C., in such a manner that a surface ofthe extension is flush with the surface of the current constrictivelayer thereby to reduce a width of the through-channel;

growing a third cladding layer comprised of AlGaAs and having the onetype of conductivity within the through-channel and internally of theextension to the current constrictive layer while the substrate is keptat a temperature of not more than 720° C., to fill the third claddinglayer inside the extension in such a manner that a surface of the thirdcladding layer is flush with the surface of the current constrictivelayer; and

successively growing a first cladding layer, an active layer, and asecond cladding layer over the substrate to form a doubleheterostructure.

According to the method of making a semiconductor light-emitting device,the extension to the current constrictive layer which has the other typeof conductivity and whose surface is flush with the surface of thecurrent constrictive layer is filled in the peripheral portion of thethrough-channel in the current constrictive layer, and the thirdcladding layer is embedded internally of the extension to the currentconstrictive layer. Therefore, when the semiconductor light-emittingdevice thus made is in operation, the width of current injection isproportionally reduced by the extension to the current constrictivelayer. With such semiconductor light-emitting device, and semiconductorlaser device in particular, therefore, the oscillation threshold valueis further reduced and, in addition, some astigmatism reduction isachieved.

Furthermore, there is provided a method of making a semiconductorlight-emitting device comprising the steps of:

forming on a surface of a GaAs substrate having one of p- andn-conductivity types a current constrictive layer comprised of GaAs orAlGaAs and having the other of the p- and n-conductivity types, thesurface being (111)B face or a face offset to the (111)B face which is amain face;

forming in the current constrictive layer a plurality ofthrough-channels of a predetermined pattern which extend from a surfaceof the current constrictive layer to the substrate;

growing third cladding layers comprised of AlGaAs and having the onetype of conductivity within the respective through-channels while thesubstrate is kept at a temperature of not more than 720° C., in such amanner that a surface of each of the third cladding layers is flush withthe surface of the current constrictive layer, thereby filling thethrough-channels; and

successively growing a first cladding layer, an active layer, and asecond cladding layer over the substrate to form a doubleheterostructure.

According to the method of making a semiconductor light-emitting device,the through-channels are formed in plurality in the current constrictivelayer, and the third cladding layers are filled in respectivethrough-channels. With such a semiconductor light-emitting device, inoperation a plurality of oscillation regions develop according to thenumber of current paths formed by the through-channels. This provides asemiconductor laser array.

Furthermore, there is provided a method of making a semiconductorlight-emitting device comprising the steps of:

forming on a surface of a GaAs substrate having one of p- andn-conductivity types a current constrictive layer comprised of GaAs orAlGaAs and having the other of the p- and n-conductivity types, thesurface being (111)B face or a face offset to the (111)B face which is amain face;

forming in the current constrictive layer a non-through channel of apredetermined pattern which is held within the current constrictivelayer;

forming in the current constrictive layer a through-channel of apredetermined pattern which extends from a surface of the currentconstrictive layer to the substrate;

growing third and fourth cladding layers comprised of AlGaAs and havingthe one type of conductivity respectively within the through-channel andnon-through channel while the substrate is kept at a temperature of notmore than 720° C., to respectively fill the through-channel andnon-through channel with the third and fourth cladding layers in such amanner that the surfaces of the third and fourth cladding layers arerespectively flush with the surface of the current constrictive layer;and

successively growing a first cladding layer, an active layer, and asecond cladding layer over the substrate to form a doubleheterostructure.

According to the method of making a semiconductor light-emitting device,the non-through channel having a depth of not more than the depth of thecurrent constrictive layer is provided in parallel with the through-holein the current constrictive layer, and the fourth cladding layer havingthe one type of conductivity is embedded in the non-through channel,with the surface of the fourth cladding layer being made flush with thesurface of the current constrictive layer. By virtue of thisarrangement, any strain exerted on the oscillation region over thethrough-channel is alleviated so that good improvement can be obtainedin a long-term reliability of the device.

Moreover, there is provided a method of making a semiconductorlight-emitting device comprising the steps of:

forming on a surface of a GaAs substrate having one of p- andn-conductivity types a current constrictive layer comprised of GaAs orAlGaAs and having the other of the p- and n-conductivity types, thesurface having (111)B face or a face offset to the (111)B face which isa main face;

forming in the current constrictive layer a through-channel of acircular pattern which extends from a surface of the currentconstrictive layer to the substrate;

growing a third cladding layer comprised of AlGaAs and having the onetype of conductivity within the through-channel while the substrate iskept at a temperature of not more than 720° C., to fill thethrough-channel with the third cladding layer in such a manner that asurface of the third cladding layer is flush with the surface of thecurrent constrictive layer;

successively growing a first cladding layer, an active layer, and asecond cladding layer over the substrate to form a doubleheterostructure; and

working the layer forming the double heterostructure to a frusto-conicalconfiguration.

According to the method of making a semiconductor light-emitting device,after the through-channel of a circular pattern which extends from thesurface of the current constrictive layer to the substrate is formed inthe current constrictive layer, the third cladding layer having the onetype of conductivity is grown within the through-channel while thesubstrate is kept at a temperature of not more than 720° C., in such amanner that the surface of the third cladding layer is flush with thesurface of the current constrictive layer, thereby filling thethrough-channel. Further, the first cladding layer, active layer, andsecond cladding layer are grown over the current constrictive layer andthird cladding layer to form the double heterostructure. Thus, a surfaceoutput type light-emitting diode is constructed. In this case, thelayers which constitute the double heterostructure are flatly formed bya known growth method, for example, MOCVD process, in a well-controlledmanner, without involving any stage of etching. Therefore, almost novariation is involved in thickness. This insures good stability inradiation intensity--applied current characteristics. Furthermore, sinceno etching process is involved after the formation of the third claddinglayer, there is no possibility of any growth interface being oxidized.This results in decreased current leakage and increased light emissionintensity. In this way, a light-emitting diode having improvedperformance characteristics can be obtained. Moreover, because of thefact that the layers forming the double heterostructure are configuredto be frusto-conical, the efficiency of light output of the device canbe enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a sectional view showing a semiconductor laser devicerepresenting a first embodiment of the present invention;

FIG. 2 is a sectional view of a semiconductor laser device representinga second embodiment of the invention;

FIG. 3 is a sectional view of a semiconductor laser device representinga third embodiment of the invention;

FIG. 4 is a diagram showing the relations between growth rates ofAlGaAs, GaInP, and AlGaInP layers on (111) B surface of a GaAs substrateand substrate temperatures;

FIGS. 5A, 5B, 5C, 5D and 5E are diagrammatic views explanatory of theprocess for manufacturing the semiconductor laser device of the firstembodiment;

FIG. 6 is a sectional view showing a semiconductor laser devicerepresenting a fourth embodiment of the invention;

FIG. 7 is a sectional view of a semiconductor laser device representinga fifth embodiment of the invention;

FIG. 8 is a sectional view of a semiconductor laser device representinga sixth embodiment of the invention;

FIG. 9 is a sectional view of a semiconductor laser device representinga seventh embodiment of the invention;

FIG. 10A is a view showing in section a light emitting diode accordingto an eighth embodiment of the invention;

FIG. 10B is a view showing in top plan the light emitting diode;

FIG. 11 is a sectional view showing a conventional semiconductor laserdevice of the effective refractive index guide type; and

FIG. 12 is a sectional view showing a conventional real refractive indexguide type semiconductor laser device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the invention will now be described in detailwith reference to the accompanying drawings. It should be noted thathatchings for some parts are omitted for the sake of simplicity in FIGS.1-3, 5A-5E, 6-9, 10A, 11 and 12.

(First Embodiment)

FIG. 1 shows a section of a semiconductor laser device representing afirst embodiment of the present invention. The semiconductor laserdevice includes a p-GaAs substrate 1 and, on (111)B face of thesubstrate 1, an n-GaAs current constrictive layer (1 μm thick) 2, ap-(Al₀.5 Ga₀.5)₀.5 In₀.5 P first cladding layer (0.2 μm thick) 3, anon-doped Ga₀.5 In₀.5 P active layer (0.05 μm thick) 4, an n-(Al₀.5Ga₀.5)₀.5 In₀.5 P second cladding layer (1.5 μm thick) 5, and an n-Ga₀.5In₀.5 P contact layer (0.5 μm thick) 6. Shown by 4a is an oscillationregion (indicated by oblique lines), and shown by 9 and 10 areelectrodes. A belt-like through-channel 2b extending perpendicularly tothe section is formed centrally in the current constrictive layer 2, anda p-Al₀.7 Ga₀.3 As third cladding layer (1.3 μm thick) 8 is embedded inthe through-channel 2b. The surface 8a of the third cladding layer 8 isflush with the surface 2a of the current constrictive layer 2.

Before the steps of fabricating the device are discussed, basicphenomenal factors will be explained. The present inventors have foundthat when an Al₀.7 Ga₀.3 As layer, a Ga₀.5 In₀.5 P layer, an (Al₀.5Ga₀.5)₀.5 In₀.5 P layer are grown by the MOCVD process on a GaAssubstrate (of either n or p conductivity type) having (111)B face as amain face, the relationship between growth rate of each layer andsubstrate temperature is as shown in FIG. 4. Materials used for layergrowth were TMG (trimethyl gallium), TMA (trimethyl aluminum), TMI(trimethyl indium), AsH₃ (arsine), and PH₃ (phosphine). In thisexperiment, for AlGaAs growth, V group element to III group elementsupply ratio (hereinafter called "V/III ratio") was set at 80, and IIIgroup element supply quantity (the sum of TMG and TMA supply quantities)was set at 1.6×10⁻⁵ mol/min. For GaInP and AlGaInP growth, V/III ratiowas set at 200, and III group element supply quantity (the sum of TMG,TMA and TMI supply quantities) was set at 2.0×10.sup. -5 mol/min.Similar experiments were carried out with cases of Al_(x) Ga_(1-x) Asand (Al_(x) Ga_(1-x))_(y) In_(1-y) P in which Al proportions x werevaried (x=0-1). Where III group element supply quantity was same, almostsame results as shown in FIG. 4 were obtained. As is apparent from FIG.4, when the substrate temperature is lower than 720° C., there is nogrowth of AlGaAs layer on (111)B face of a GaAs substrate. GaInP andAlGaInP layers can grow over a wide temperature range (650° to 750° C.),and their growth rates are almost constant, being not dependent on thesubstrate temperature. The process for manufacturing the device of theinvention utilizes this phenomenon.

The relationship between growth rate on (111)B face of a GaAs substrateand substrate temperature has been known with respect to GaAs growth(Journal of Crystal Growth, Vol. 94 (1989) p.p. 203-207 (hereinaftercalled "Reference 1"). FIG. 1 of the Reference 1 shows that the growthrate of GaAs, as is the case with the growth rate shown for Al_(x)Ga_(1-x) As in FIG. 4 of the present application, is zero when thesubstrate temperature is lower than 720° C. and crystal growth begins ata substrate temperature of more than 720° C. However, the descriptiongiven in the Reference 1 concerns only the characteristics of GaAsgrowth on (111)B face of GaAs substrate, and does not relate to thegrowth of AlGaAs, GaInP, and AlGaInP on (111)B face of GaAs substrate.As will be described in detail hereinafter, the advantageous effect ofthe present invention can only be achieved through the use of AlGaAs andnot GaAs as material for third cladding layer 8 shown in FIG. 1. Inother words, the present invention cannot be derived from Reference 1,and the invention has been developed only through the discovery of thephenomenal fact on the growth of AlGaAs, GaInP, and AlGaInP as shown inFIG. 4.

For the purpose of making the semiconductor laser device, as FIG. 5Ashows, an n-GaAs current constrictive layer 2 is grown 1 μm thick on(111)B face of p-GaAs substrate 1 by using liquid phase growingtechnique. Then, as FIG. 5B shows, etching is carried out to formthrough-channels 2b, 2b, . . . of 4 μm wide and 1.3 μm deep which extendfrom the surface 2a of the current constrictive layer 2 to the p-GaAssubstrate. In the present example, the orientation of eachthrough-channel 2b was [100] direction. Then, as FIGS. 5C and 5D show, ap-Al₀.7 Ga₀.3 As cladding layer 8 was grown over the substrate 1 by theMOCVD process. Growing conditions were: substrate temperature, 700° C.;and V/III ratio, 80. As earlier explained with reference to FIG. 4,under these growth conditions the rate of growth on (111)B face of GaAssubstrate 1 is almost zero. Therefore, AlGaAs layer does not grow at thebottom of through-channel 2b nor does it grow on the surface of then-GaAs current constrictive layer 2. Instead, as FIG. 5C shows, theAlGaAs layers 8 grow inwardly from the side walls of through-channel 2band, as FIG. 5D shows, the through-channel is entirely filled whenfronts of the AlGaAs layers growing from the upper edges of the sidewall meet together. As a result, the surface 8a of each cladding layer 8becomes flush with the surface 2a of the current constrictive layer 2,so that the surface side of the substrate 1 becomes flat. Subsequently,as FIG. 5E shows, a p-AlGaInP cladding layer 3, a non-doped GaInP activelayer 4, an n-AlGaInP cladding layer 5, and an n-GaInP contact layer 6were grown on the surface side of the substrate by the MOCVD process.Growth conditions were: substrate temperature, 700° C.; and V/III ratio,200. In this case, the AlGaInP layers 3, 5 and GaInP layers 4, 6 exhibita growth pattern different from that seen with the AlGaAs layer, thatis, growth occurs on the (111)B face as well (growth rate is 1.7 μm/hourunder the aforesaid growth conditions). Then, electrodes 9, 10 wereformed respectively on the underside of the substrate 1 and on thesurface of the contact layer 6. Finally, the product was split alongeach chain line in FIG. 5E into chips to give the same semiconductorlaser device as shown in FIG. 1.

According to the above described method, p-AlGaInP cladding layer 3 isgrown by the MOCVD process in a well controlled manner and is notsubjected to etching. Therefore, little or no variation occurs withrespect to the thickness d of cladding layer 3. This leads to goodstability in the fundamental mode. The fact that no etching step isinvolved eliminates the possibility of oxidation with any growthinterface. Current leakage is decreased, and oscillation threshold limitis lowered. The cladding layer 3 on the current constrictive layer 2 isso thin that higher-order mode loss can be moderately maintained. Thisresults in good improvement in the kink level. True, semiconductor laserdevices thus fabricated, in noncoat condition and with resonator lengthof 400 μm, had an oscillation threshold limit of 40 mA and oscillated upto 50 mW without kink. Its oscillation wavelength was 679 nm during 50mW output. As compared with the prior art semiconductor laser deviceshown in FIG. 11 which, in the condition of noncoat and resonator length400 μm, had an oscillation threshold value of 45 mA and a kink level of25 mW, this is considerable improvement or two-fold improvement in kinklevel.

For purposes of comparison, a device having a sectional constructionidentical with the device shown in FIG. 1 was made using GaAs asmaterial for a third cladding layer and utilizing the phenomenon shownin FIG. 1 of the Reference 1. However, laser oscillation was notachieved with this device for comparison. The reason was that since thethird cladding layer was made of GaAs, it was not possible to obtain anygain necessary for laser oscillation. This tells that the material forthe third cladding layer 8 must be AlGaAs as explained above.

(Second Embodiment)

FIG. 2 shows a section of a semiconductor laser device representing asecond embodiment of the invention. This semiconductor laser deviceincludes a p-GaAs substrate 11 and, on (111)B face of the substrateoffset by 2° to a direction of [100], an n-GaAs current constrictivelayer (1 μm thick) 12, a p-(Al₀.7 Ga₀.3)₀.5 In₀.5 P first cladding layer(0.2 μm thick) 13, a non-doped (Al₀.1 Ga₀.9)₀.5 In₀.5 P active layer(0.05 μm thick) 14, an n-(Al₀.7 Ga₀.3)₀.5 In₀.5 P second cladding layer(1.5 μm thick) 15, an n-Ga₀.5 In₀.5 P contact layer (0.5 μm thick) 16,and an n-GaAs contact layer (0.1 μm thick) 17. Shown by 14a is anoscillation region, and shown by 19 and 20 are electrodes. A belt-likethrough-channel 12b extending perpendicularly to the section is formedcentrally in the current constrictive layer 12, and a p-Al₀.7 Ga₀.3 Asthird cladding layer (1.3 μm) 18 is embedded in the through-channel 12b.The surface 18a of the cladding layer 18 is flush with the surface 12aof the current constrictive layer 12.

This semiconductor laser device is different from the one of the firstembodiment in that the layers 12, 13 . . . are formed on (111)B faceinclined by 2° to the direction of [100]and in that the n-Ga contactlayer 17 is provided over the n-GaInP contact layer 16. The provision ofthe n-GaAs contact layer 17 facilitates ohmic contact with the electrode20, whereby the resistance of the device can be reduced. Further, adouble heterostructure consists of the p-(Al₀.7 Ga₀.3)₀.5 In₀.5 Pcladding layer 13, the non-doped (Al₀.1 Ga₀.9)₀.5 In₀.5 P active layer14, the n-(Al₀.7 Ga₀.3)₀.5 In₀.5 P cladding layer 15. This arrangementprovides an oscillation wavelength of 650 nm.

In fabricating the device, as is the case with the first embodiment, thesubstrate temperature was set at 700° C., at which temperature wereformed layers of from cladding layer 18 to contact layer 17. Despite thefact that layers were formed at an orientation offset by 2° from (111)Bface of the p-GaAs substrate 11, the surface 18a of the cladding layer18 could be made flush with the surface 12a of the current constrictivelayer 12. The contact layer 17 was grown on the surface of the contactlayer 16 ((111)B face of GaAs) in such a condition that the substratetemperature was raised to 740° C. so as to enable GaAs to grow on (111)Bface as well.

This semiconductor laser device, as was the case with the device of thefirst embodiment, exhibited good fundamental mode stability. Currentleakage was decreased; oscillation threshold limit was lowered; and kinklevel was enhanced. A coating of Al₂ O₃, of λ/2 thickness (λ representsoscillation wavelength) was applied to each end face of a chip ofresonator length of 500 μm. At this condition, the device exhibitedsatisfactory characteristics: oscillation threshold value, 50 mA; andkink level, 45 mW.

(Third Embodiment)

FIG. 3 shows a section of a semiconductor laser device representing athird embodiment of the invention. The semiconductor laser deviceincludes a p-GaAs substrate 31 and, on (111)B face of the p-GaAssubstrate 31, an n-GaAs current constrictive layer (1 μm thick) 32, ap-Al₀.7 Ga₀.3 As third cladding layer (0.02 μm thick) 38', a p-(Al₀.5Ga₀.5)₀.5 In₀.5 P first cladding layer (0.2 μm thick) 33, a non-dopedGa₀.38 In₀.62 P active layer (0.02 μm thick) 34, an n-(Al₀.5 Ga₀.5)₀.5In₀.5 P second cladding layer (1.5 μm thick) 35, and an n-Ga₀.5 In₀.5 Pcontact layer (0.5 μm thick) 36. Shown by 34a is an oscillation region,and shown by 39 and 40 are electrodes. A belt-like through-channel 32bextending perpendicularly to the section is formed centrally in thecurrent constrictive layer 32, and a p-Al₀.7 Ga₀.3 As third claddinglayer (1.3 μm thick) 38 is embedded in the through-channel 32b. Thecladding layer 38' is an extended portion which is connected integrallywith the cladding layer 38, and coves the surface of the currentconstrictive layer 32. The surface 38a of the cladding layer 38 is flushwith the surface 32a of the current constrictive layer 32.

This semiconductor laser device is different from the device of thefirst embodiment in that the composition of the active layer 34 isnon-doped Ga₀.38 In₀.62 P to give some distorted effect, and in that thesubstrate temperature was set at 730° C. during the growth of claddinglayer 38 thereby to allow slight growth of AlGaAs layer 38' on thesurface (GaAs (111)B face) 32a of the current constrictive layer 32 onboth sides of the through-channel 32b. In consequence, the active layer34 is slightly bent over the edges of the through-channel 32b as shown.Thus, the device has a waveguide structure having the characteristic ofan effective refractive index guide utilizing the light absorption ofthe substrate (current constrictive layer) and the characteristic of areal refractive index guide structure utilizing bending of the activelayer, that is, the advantages of both of the two prior art arrangementsshow in FIGS. 11 and 12. In other words, the semiconductor laser devicecan reduce mode loss with respect to fundamental mode and enhance modeloss with respect to higher-order mode, thereby further stabilizing thefundamental mode. Further, as the device of the first embodiment does,this device provides for current leakage reduction, oscillationthreshold value decrease, and kink level improvement.

Under the conditions of resonator length 600 μm, and reflection factors,front side 8% and rear side 70%, the device exhibited an oscillationthreshold value of 55 mA and a kink level of 220 mW (oscillationwavelength 690 nm). This indicates some twofold improvement as comparedwith the kink level (about 120 mW) of the prior art device shown in FIG.11 in which same double heterostructure as the present embodiment isemployed.

To fabricate the device, a through-channel 32b is formed in the currentconstrictive layer 32 in the same way as in the first embodiment, andthen the substrate temperature is set at 730° C. at which temperatureare formed layers including cladding layer 38 through contact layer 36.With the substrate temperature so set at 730° C., the cladding layer 38was grown within the through-channel 32b in such a manner that itssurface was flush with the surface of the current constrictive layer 32,so as to fill in the through-groove 32b. Also, an extension 38' to thecladding layer 38 which was thinner than that portion of the claddinglayer 38 which filled the through-channel 32b was grown on the surfaceof the current constrictive layer 32. Further, layers 33, 34, 35 . . .were grown over the cladding layer 38 inclusive of the extension 38' ata moderate rate of growth. Aforesaid waveguide structure was thusformed. In this case, a temperature range of 720° to 740° C. is suitablefor the substrate temperature. If the temperature is less than 720° C.,it is not possible to grow the extension 38'. If the temperature is morethan 740° C., the extension 38' grows excessively thick.

(Fourth Embodiment)

FIG. 6 shows a section of a semiconductor laser device representing afourth embodiment of the invention. This semiconductor laser deviceincludes a p-GaAs substrate 41 and, on (111)B face of the p-GaAssubstrate 41, a current constrictive layer 42 (1 μm thick) consisting oftwo layers 42', 42", a p-(Al₀.5 Ga₀.5)₀.5 In₀.5 P first cladding layer(0.2 μm thick) 43, a non-doped Ga₀.5 In₀.5 P active layer (0.05 μmthick) 44, an n-(Al₀.5 Ga₀.5)₀.5 In₀.5 P second cladding layer (1.5 μmthick) 45, and an n-Ga₀.5 In₀.5 P contact layer (0.5 μm thick). Shown by44a is an oscillation region, and shown by 49, 50 are electrodes. Athrough-channel 42b extending perpendicularly to the section is formedcentrally in the current constrictive layer 42, and a p-Al₀.7 Ga₀.3 Asthird cladding layer (1.3 μm thick) is filled in this through-channel42b. The surface 48a of the cladding layer 48 is flush with the surface42a of the current constrictive layer 42.

This semiconductor laser device is different from the device of thefirst embodiment in that the current constrictive layer 42 is of atwo-layer construction consisting of n-Al₀.1 Ga₀.9 As (0.9 μm thick) 42'and n-GaAs (0.1 μm thick) 42". To fabricate this semiconductor laserdevice, after n-Al₀.1 Ga₀.9 As (0.9 μm thick) 42' and n-GaAs (0.1 μmthick) 42" are formed, a through-channel 42b is formed centrally in thecurrent constrictive layer 42 which extends from the surface of thelayer 42" to the substrate 41. Then, the AlGaAs layer 48 is grown on thesubstrate 41 by MOCVD process. In the same way as in the firstembodiment, selective growth occurred at a substrate temperature of lessthan 720° C. such that only the interior of the through-channel 42b wasfilled even when the n-Al₀.1 Ga₀.9 As layer 42' was exposed on thethrough-channel 42b side surface of the current constrictive layer 42.Such selective growth continued until the Al proportion of the AlGaAscurrent constrictive layer 42 reached zero or at least 0.3.Subsequently, layers 43, 44, 45 . . . were grown by MOCVD process. Inthis way, it is possible to form an effective refractive index guidestructure utilizing light absorption of the current constrictive layer42 and substrate 41, in a well controlled manner.

Just as the devices of the first and second embodiments did, thissemiconductor laser device proved that it was effective for fundamentalmode stabilization, current leak reduction, oscillation threshold valuedecrease, and kink level improvement.

(Fifth Embodiment)

FIG. 7 shows a section of a semiconductor laser device representing afifth embodiment of the invention. This semiconductor laser deviceincludes a p-GaAs substrate 51 and, on (111)B face of the p-GaAssubstrate 51, n-GaAs current constrictive layers (1 μm thick) 52, 52', ap-(Al₀.5 Ga₀.5)₀.5 In₀.5 P first cladding layer (0.2 μm thick) 53, anon-doped Ga₀.5 In₀.5 P active layer (0.05 μm thick) 54, an n-(Al₀.5Ga₀.5)₀.5 In₀.5 P second cladding layer (1.5 μm thick) 55, and ann-Ga₀.5 In₀.5 P contact layer (0.5 μm thick) 56. Shown by 54a is anoscillation region, and shown by 59, 60 are electrodes. A belt-likethrough-channel 52b is formed centrally in the current constrictivelayer 52 which extends perpendicularly to the section. An n-GaAsextension 52' of the current constrictive layer is embedded in an innerperipheral portion of the through-channel 52b, and a p-Al₀.7 Ga₀.3 Asthird cladding layer (1.3 μm thick) is embedded internally of thecurrent constrictive layer extension 52'. The surface 58a of thecladding layer 58 is flush with the surfaces 52a, 52a' of the currentconstrictive layers 52, 52'.

In fabricating this semiconductor laser device, after a through-channel(4 μm wide) 52b is formed, an n-GaAs current constrictive layerextension 52' is laterally grown until the remaining width of thethrough-channel 52b is 2.5 μm, and then an AlGaAs fill layer 58 isgrown. Subsequently, in the same way as in the first embodiment, layers53, 54, 55 . . . are grown.

This semiconductor laser device, just as the device of the firstembodiment does, has an effective refractive index guide structureformed in a well controlled manner, and provides for good fundamentalmode stability, current leak reduction, oscillation threshold valuedecrease, and kink level enhancement. Furthermore, the provision of thecurrent constrictive layer extension 52' formed in the through-channel52b' so as to reduce the width of current injection path results ingreater reduction of oscillation threshold value than in the case of thedevice of the first embodiment, and further in reduced astigmatism.Whereas, under conditions of non-coat, resonator length of 400 μm, thedevice of the first embodiment exhibited an oscillation threshold valueof 40 mA and an astigmatism of 5 μm (3 mWh), the semiconductor laserdevice of the present embodiment exhibited an oscillation thresholdvalue of 30 mA and an astigmatism value of 0 μm (3 mWh) under the sameconditions.

(Sixth Embodiment)

FIG. 8 shows a section of a sixth embodiment of the invention. Thissemiconductor device includes a p-GaAs substrate 61 and, on (111)B faceof the p-GaAs substrate 61, an n-GaAs current constrictive layer (1 μmthick) 62, a p-(Al₀.5 Ga₀.5)₀.5 In₀.5 P first cladding layer (0.2 μmthick) 63, a non-doped Ga₀.5 In₀.5 P active layer (0.05 μm thick) 64, ann-(Al₀.5 Ga₀.5)₀.5 In₀.5_(P) second cladding layer (1.5 μm thick) 65,and an n-Ga₀.5 In₀.5 P contact layer (0.5 μm thick) 66. Shown by 64a isan oscillation region, and shown by 69, 70 are electrodes. Threebelt-like through-channels 62b, 62b, 62b (3.5 μm wide each, arranged at5.5 μm pitch) which extend perpendicularly to the section arerespectively formed centrally and on both sides of the currentconstrictive layer 62. A p-Al₀.7 Ga₀.3 As third cladding layer (1.3 μmthick) 68 is filled in each of the through-channels 62b. The surface 68aof the cladding layer 68 is flush with the surface 62a of the currentconstrictive layer 62.

This semiconductor laser device is identical with the device of thefirst embodiment insofar as layer arrangement is concerned, but isdifferent from the latter in that it includes a plurality ofthrough-channels 62b formed in the current constrictive layer 62 whichserve as current path, and accordingly it constitutes a semiconductorlaser array having a plurality of oscillation regions 64a. With thissemiconductor laser device, oscillation at 180° phase mode was observedup to such a high output as 350 mW.

To fabricate this semiconductor device, after current constrictive layer62 is formed on the substrate 61, a plurality of through-channels 62b,62b, 62b are formed simultaneously in the current constrictive layer 62.Thereafter, in the same way as in the first embodiment, third claddinglayers 68 are filled in the respective through-channels 62b. Then,layers 63, 64, 65 . . . which make a double heterostructure are grown.

(Seventh Embodiment)

FIG. 9 shows a section of a semiconductor laser device representing aseventh embodiment of the invention. This semiconductor laser deviceincludes a p-GaAs substrate 71 and, on (111)B face of the p-GaAssubstrate 71, an n-GaAs current constrictive layer (1 μm thick) 72, ap(Al₀.5 Ga₀.5)₀.5 In₀.5 P first cladding layer (0.2 μm thick) 73, anon-doped Ga₀.5 In₀.5 P active layer (0.05 μm thick) 74, an n-(Al₀.5Ga₀.5)₀.5 In₀.5 P second cladding layer (1.5 μm thick) 75, and ann-Ga₀.5 In₀.5 P contact layer (0.5 μm thick) 76. Shown by 74a is anoscillation region, and shown by 79 and 80 are electrodes. A belt-likethrough-channel 72b extending perpendicularly to the section is formedcentrally in the current constrictive layer 72, and a p-Al₀.7 Ga₀.3 Asthird cladding layer (1.3 μm) 78 is filled in the through-channel 72b(which serves as a current path). Belt-like non-through channels 72' areformed in plurality at a predetermined pitch at both sides of thecurrent constrictive layer 72. Filled in respective non-through channels72b' are p-Al₀.7 Ga₀.3 As fourth cladding layers. The surface of eachcladding layer 78, 78' is flush with the surface 72a of the currentconstrictive layer 72.

To manufacture the semiconductor laser device, the current constrictivelayer 72 is first formed on the substrate 71, and then non-throughchannels 72b', . . . which are to be retained within the currentconstrictive layer 72 are formed in the current constrictive layer 72.Then, a through-channel 72b which extends from the surface of thecurrent constrictive layer 72 to the substrate 71 is formed in thecurrent constrictive layer 72. Subsequently, in the same way as in thefirst embodiment, the substrate 1 is kept at a temperature of 700° C. Inthis condition, cladding layers 78, 78', . . . are grown simultaneouslywithin the through-channel 72b and non-through channels 72b' in such amanner that their respective surfaces are flush with the surface of thecurrent constrictive layer 72, to thereby fill the through-channel 72band non-through channels 72b'. After that, in the same way as in thefirst embodiment, cladding layer 73, active layer 74, and cladding layer75 are grown all over.

This semiconductor laser device is identical with the device of thefirst embodiment in layer construction, except that through-channel 72band non-through channels 72b' . . . are formed in plurality in thecurrent constrictive layer 72. The centrally located through-channel 72bextends from the surface of the current constrictive layer 72 to thesubstrate 71, while the non-through channels 72b' are retained withinthe current constrictive layer 72. Through-channel 72b is the onlythrough-channel for defining an oscillation region, while otherchannels, that is, non-through channels 72b', . . . are intended toeliminate possible distortion arising from the layer structure. In thesemiconductor laser device of the first embodiment which is shown inFIG. 1, all strain is applied to that portion of the active layer 74which is located above the edges of the through-channel 2b (boundary ofthe oscillation region 4a). In the present embodiment, the presence ofnon-through channels 72b' (and AlGaAs layers filled in these channels),in addition to the through-channel 72b, provides for the dispersion ofthe strain exerted upon the active layer 74 into the non-throughchannels 72b', thus alleviating the strain of the oscillation region74a, which fact insures good long-term reliability of the device.

(Eighth Embodiment)

FIGS. 10A and 10B show a surface-output type light emitting dioderepresenting eighth embodiment of the invention, FIG. 10A being asectional view, FIG. 10B being a top plan view with respect to FIG. 10Asection. This light-emitting diode includes a p-GaAs substrate 81 and,on (111)B face of the p-GaAs substrate 81, an n-GaAs currentconstrictive layer 82, a p-(Al₀.7 Ga₀.3)₀.5 In₀.5 P P first claddinglayer 83, a non-doped (Al₀.45 Ga₀.55)₀.5 In₀.5 P active layer 84, ann-(Al₀.7 Ga₀.3)₀.5 In₀.5 P second cladding layer 85, and an n-Ga₀.5In₀.5 P contact layer 86. Shown by 89, 90 are electrodes. Athrough-channel 82b of a circular pattern is formed centrally in thecurrent constrictive layer 82, and in this through-channel 82b is filleda p-Al₀.7 Ga₀.3 As third cladding layer 88. The surface 88a of thecladding layer 88 is flush with the surface 82a of the currentconstrictive layer 82. A center portion of the cladding layer 85 isworked to a frusto-conical pattern by the ion milling technique.

The current constrictive layer 82, through-channel 82b, and claddinglayer 88 are formed in substantially the same way as in the firstembodiment. Therefore, the cladding layer 83, active layer 84, andcladding layer 85 which constitute a double heterostructure are formedin a well controlled manner, and this provides for good stability inlight emission intensity--applied current characteristics. No etchingstep is involved after the formation of the cladding layer 88 and,therefore, it is unlikely that any growth interface will becomeoxidized. Thus, possible current leakage is reduced and light emissionintensity is increased. In this way, improvement can be effected withrespect to light-emitting diode characteristics. A contact layer 86 andan upper electrode 90 are defined by a small circular pattern disposedon a frusto-conical portion of the cladding layer 85. This provides forincreased efficiency of drawing light from the device surface.

A molded package of 5 mm dia. incorporating the light-emitting diode,when energized 20 mA, exhibited a luminous intensity of 4 candela (i.e., conventionally of the order of 0.3 candela) at a wavelength of 555nm.

In the foregoing embodiments, the GaAs substrate is of the p-type, butit is needless to say that the substrate is not so limited. The GaAssubstrate may be of either p-conductivity type or n-conductivity type,and the conductivity type of each respective layer grown may bedetermined depending upon the conductivity type of the GaAs substrate.The wave band of laser oscillation may be selected from the wave bandrange of red to orange, by suitably selecting the composition of theAlGaInP active layer. The active layer need not necessarily benon-doped, but may be of the p-type or of the n-type. For the doublehetero layer structure, where so required, may be employed an SCHstructure (separate confinement heterostructure) including a guide layeras required, or a multiquantum well structure or multiquantum barrierstructure. A GaInP or GaAs contact layer may be provided as required.The GaAs substrate need not necessarily be oriented in a just directioninsofar as it has (111)B face as a main face, but may be oriented somedegrees off in [100] or [011] directions. For layer growth after theAlGaAs layer is filled in the current constrictive layer, MOCVD processis preferably employed, but other vapor phase growing methods may beemployed instead, including molecular beam epitaxy, atomic layerepitaxy, and chemical beam epitaxy methods.

As is clear from the foregoing description, a semiconductorlight-emitting device of the invention includes a substrate having oneof p- and n- conductivity types, a current constrictive layer formed onthe surface of the substrate and having the other of the p- and n-conductivity types, the current constrictive layer having athrough-channel extending to the surface of the substrate in a directionperpendicular to the surface of the substrate for defining a currentpath extending perpendicularly to the surface of the substrate, and adouble heterostructure formed on the current constrictive layerincluding a first cladding layer, an active layer and a second claddinglayer, wherein the through-channel is of a belt-like pattern whichextends perpendicularly to the surface of the substrate. Therefore,according to this arrangement, it is possible to provide a refractiveindex guide type semiconductor laser device. The semiconductor laserdevice has a third cladding layer of the one conductivity type filled inthe through-channel of the current constrictive layer, the surface ofthe third cladding layer being flush with the surface of the currentconstrictive layer. The first cladding layer, active layer and secondcladding layer which constitute the double heterostructure are formed bya known growth method, for example, MOCVD process, flatly over thecurrent constrictive and third cladding layers in a well-controlledmanner, without involving any process of etching. Therefore, the firstcladding layer, active layer and second cladding layer involve almost novariation in thickness. This insures better stability in the fundamentalmode of laser oscillation, as compared with any conventionalsemiconductor laser device. The fact that no etching process is involvedafter the formation of the third cladding layer eliminates thepossibility of any growth interface being oxidized. This results indecreased current leakage and lowered oscillation threshold limit. Thefirst cladding layer is usually designed to be relatively thin and in nocase does this result in decreased higher-order mode loss. Therefore,good improvement is achieved in kink level. In this way, a semiconductorlaser device having improved performance characteristics can beobtained.

Where the third cladding layer has an extended portion covering thesurface of the current constrictive layer, the extended portion having athickness set thinner than the portion filled in the through-channel,the active layer is so formed that it is slightly bent adjacent the edgeof the through-channel, when the double heterostructure is formed as bythe MOCVD process. As a result, a waveguide arrangement is obtainedwhich has both the characteristic of an effective refractive index guidestructure utilizing the light absorption of the substrate (currentconstrictive layer) and the characteristic of a real refractive indexguide structure utilizing the bend of the active layer. This providedfor mode loss reduction with respect to the fundamental mode and modeloss enhancement with respect to the higher-order mode, with the resultthat the fundamental mode is further stabilized.

Where an extension to the current constrictive layer having the othertype of conductivity is filled in a peripheral portion of thethrough-channel, the surface of the extension being flush with thesurface of the current constrictive layer, and the third cladding layeris filled internally of the extension to the current constrictive layerwithin the through-channel, during operation of the device, the width ofcurrent injection can be proportionally reduced by the extension to thecurrent constrictive layer. Therefore, the oscillation threshold valueis further reduced and, in addition, some astigmatism reduction isachieved.

Where a plurality of through-channels are formed in the currentconstrictive layer, with the third cladding layers being embedded in therespective through-channels, during operation of the device, a pluralityof oscillation regions develop according to the number of current pathsformed by the through-channels. This provides a semiconductor laserarray.

Where at least one non-through channel is formed in parallel with thethrough-channel in the current constrictive layer to a depth not greaterthan the depth of the current constrictive layer, and a fourth claddinglayer having the one type of conductivity is filled in the non-throughchannel, the surface of the fourth cladding layer being flush with thesurface of the current constrictive layer, any strain which is exertedupon the active layer because of layers being stacked on the substratecan be distributed over the non-through channel. Thus, the strainapplied to the oscillation region over the through-channel can bealleviated so that good improvement is achieved in the long-termreliability of the device.

The semiconductor light-emitting device of an embodiment of theinvention includes a substrate having one of p- and n- conductivitytypes, a current constrictive layer formed on the surface of thesubstrate and having the other of the p- and n- conductivity types, thecurrent constrictive layer having a through-channel extending to thesurface of the substrate in a direction perpendicular to the surface ofthe substrate for defining a current path extending perpendicularly tothe surface of the substrate, and a double heterostructure formed on thecurrent constrictive layer including a first cladding layer, an activelayer and a second cladding layer, wherein the through-channel is of acircular pattern. According to this arrangement, it is possible toprovide a surface output type light-emitting diode. The light-emittingdiode comprises a third cladding layer having the one type ofconductivity and filled in the through-channel of the currentconstrictive layer, the surface of the third cladding layer being flushwith the surface of the current constrictive layer. Therefore, the firstcladding layer, active layer and second cladding layer which constitutethe double heterostructure are formed by a known growth method, forexample, MOCVD process, flatly over the current constrictive and thirdcladding layers in a well-controlled manner, without involving anyprocess of etching. Therefore, the first cladding layer, active layerand second cladding layer involve almost no variation in thickness. Thisinsures good stability in radiation intensity--applied currentcharacteristics. The fact that no etching process is involved after theformation of the third cladding layer eliminates the possibility of anygrowth interface being oxidized. This results in decreased currentleakage and increased light emission intensity. In this way, alight-emitting diode having improved performance characteristics can beobtained.

Where the layers forming the double heterostructure are formed to befrusto-conical, the efficiency of light output of the device can beenhanced.

Also, the substrate is a GaAs substrate having (111)B face or a faceoffset to the (111)B face which is a main face; the current constrictivelayer is comprised of GaAs or AlGaAs; and the third cladding layer iscomprised of AlGaAs. In this case, it is possible to grow the thirdcladding layer comprised of AlGaAs having the one type of conductivitywithin the through-channel while the substrate is kept at a temperatureof not more than 720° C. to fill the through-channel with the thirdcladding layer in such a manner that the surface of the third claddinglayer becomes flush with the surface of the current constrictive layer.Therefore, the first cladding layer, active layer, and second claddinglayer which constitute a double heterostructure can be grown by theknown growth technique flatly over the current constructive layer andthird cladding layer in a well controlled manner.

According to a method of making a semiconductor light-emitting device ofan embodiment of the present invention, on a surface of a GaAs substratehaving one of p- and n-conductivity types is formed a currentconstrictive layer comprised of GaAs or AlGaAs and having the other ofthe p- and n-conductivity types, the substrate surface being (111)B faceor a face offset to the (111)B face which is a main face. Athrough-channel of a predetermined pattern which extends from thesurface of the current constrictive layer to the substrate is thenformed in the current constrictive layer. Then, a third cladding layercomprised of AlGaAs and having the one type of conductivity is grownwithin the through-channel while the substrate is kept at a temperatureof not more than 720° C. This enables the third cladding layer to begrown so that its surface becomes flush with the surface of the currentconstrictive layer thereby to fill the through-channel. Therefore, thefirst cladding layer, active layer, and second cladding layer can beformed flatly over the third cladding layer and current constrictivelayer in a well controlled manner to form a double heterostructure.Thus, it is now possible to fabricate semiconductor light-emittingdevices, such as semiconductor laser devises and light-emitting diodes,which have improved performance characteristics as compared withconventional devices of the kind.

According to the method of making a semiconductor light-emitting deviceof an embodiment, after a through-channel is formed in a currentconstrictive layer, a third cladding layer comprised of AlGaAs andhaving one type of conductivity is grown while a substrate is keptwithin a temperature range of 720° C. to 740° C. so as to fill thethrough-channel in such a manner that a surface of portion of the thirdcladding layer which fills the through-channel is flush with a surfaceof the current constrictive layer and that the third cladding layer hasan extended portion overlying the surface of the current constrictivelayer and being thinner than the fill portion. Therefore, when layersconstituting a double heterostructure are formed on the currentconstrictive layer using, for example, the MOCVD technique, an activelayer is formed to be slightly bent adjacent an edge of thethrough-channel. Thus, the semiconductor light-emitting device made hasa waveguide construction featuring both the characteristic of aneffective refractive index guide structure utilizing the lightabsorption of the substrate (current constrictive layer) and thecharacteristic of a real refractive index guide structure utilizing thebend of the active layer. Therefore, the semiconductor laser device canreduce mode loss relative to the fundamental mode and increase mode lossrelative to the higher-order mode, so that the fundamental mode isfurther stabilized. Furthermore, possible current leaks are reduced andthe oscillation threshold limit is lowered.

According to the method of making a semiconductor light-emitting deviceof an embodiment, an extension to a current constrictive layer which hasthe other type of conductivity and whose surface is flush with a surfaceof the current constrictive layer is filled inside a through-channel inthe current constrictive layer, and the third cladding layer is filledinternally of the extension to the current constrictive layer.Therefore, when the semiconductor light-emitting device thus made is inoperation, a width of current injection is proportionally reduced by theextension to the current constrictive layer. With such semiconductorlight-emitting device, and semiconductor laser device in particular,therefore, the oscillation threshold value is further reduced and, inaddition, some astigmatism reduction is achieved.

According to the method of making a semiconductor light-emitting deviceof an embodiment, through-channels are formed in plurality in a currentconstrictive layer, and third cladding layers are filled in respectivethrough-channels. In operation of such a semiconductor light-emittingdevice, a plurality of oscillation regions develop according to thenumber of current paths formed by the through-channels. This provides asemiconductor laser array.

According to the method of making a semiconductor light-emitting deviceof an embodiment, at least one non-through channel having a depth of notmore than a depth of a current constrictive layer is provided inparallel with a through-channel in the current constrictive layer, and afourth cladding layer having the one type of conductivity is embedded inthe non-through channel, with a surface of the fourth cladding layerbeing made flush with a surface of the current constrictive layer. Byvirtue of this arrangement, any strain exerted on an oscillation regionover the through-channel is alleviated so that good improvement can beobtained in the long-term reliability of the device.

According to the method of making a semiconductor light-emitting deviceof an embodiment, after a through-channel of a circular pattern whichextends from a surface of a current constrictive layer to a substrate isformed in the current constrictive layer, a third cladding layer havingone type of conductivity is grown within the through-channel while thesubstrate is kept at a temperature of not more than 720° C., in such amanner that a surface of the third cladding layer is flush with thesurface of the current constrictive layer, thereby filling thethrough-channel. Further, a first cladding layer, an active layer, and asecond cladding layer are grown over the current constrictive layer andthird cladding layer to form a double heterostructure. Thus, a surfaceoutput type light-emitting diode is constructed. In this case, thelayers which constitute the double heterostructure are flatly formed bya known growth method, for example, MOCVD process, in a well-controlledmanner, without involving any process of etching. Therefore, almost novariation is involved in thickness. This insures good stability inradiation intensity--applied current characteristics. Furthermore, sinceno etching process is involved after the formation of the third claddinglayer, there is no possibility of any growth interface being oxidized.This results in decreased current leakage and increased light emissionintensity. In this way, a light-emitting diode having improvedperformance characteristics can be obtained. Moreover, because of thefact that the layers forming the double heterostructure are formed to befrusto-conical, the efficiency of light output of the device can beenhanced.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A method of making a semiconductor light-emittingdevice comprising the steps of:forming on a surface of a GaAs substratehaving one of p- and n-conductivity types a current constrictive layercomprised of GaAs or AlGaAs and having the other of the p- andn-conductivity types, the surface being (111)B face or a face offset tothe (111)B face which is a main face; forming in the currentconstrictive layer a through-channel of a predetermined pattern whichextends from a surface of the current constrictive layer to thesubstrate; growing a third cladding layer comprised of AlGaAs and havingthe one type of conductivity within the through-channel while thesubstrate is kept at a temperature of not more than 720° C. to fill thethrough-channel with the third cladding layer in such a manner that thesurface of the third cladding layer becomes flush with the surface ofthe current constrictive layer; and successively growing a firstcladding layer, an active layer, and a second cladding layer over thesubstrate to form a double heterostructure.
 2. A method of making asemiconductor light-emitting device comprising the steps of:forming on asurface of a GaAs substrate having one of p- and n-conductivity types acurrent constrictive layer comprised of GaAs or AlGaAs and having theother of the p- and n-conductivity types, the surface being (111)B faceor a face offset to the (111)B face which is a main face; forming in thecurrent constrictive layer a through-channel of a predetermined patternwhich extends from a surface of the current constrictive layer to thesubstrate; growing a third cladding layer comprised of AlGaAs and havingthe one type of conductivity while the substrate is kept within atemperature range of 720° C. to 740° C. in such a manner that oneportion of the third cladding layer which fills the through-channel hasa surface flush with the surface of the current constrictive layer andthat the third cladding layer has an extended portion overlying thesurface of the current constrictive layer and being thinner than thefill portion; and successively growing a first cladding layer, an activelayer, and a second cladding layer over the substrate to form a doubleheterostructure.
 3. A method of making a semiconductor light-emittingdevice comprising the steps of:forming on a surface of a GaAs substratehaving one of p- and n-conductivity types a current constrictive layercomprised of GaAs or AlGaAs and having the other of the p- andn-conductivity types, the surface being (111)B face or a face offset tothe (111)B face which is a main face; forming in the currentconstrictive layer a through-channel of a predetermined pattern whichextends from a surface of the current constrictive layer to thesubstrate; growing in a peripheral portion of the through-channel anextension to the current constrictive layer which is comprised of GaAsor AlGaAs and has the other type of conductivity while the substrate iskept at a temperature of not more than 720° C., in such a manner that asurface of the extension is flush with the surface of the currentconstrictive layer thereby to reduce a width of the through-channel;growing a third cladding layer comprised of AlGaAs and having the onetype of conductivity within the through-channel and internally of theextension to the current constrictive layer while the substrate is keptat a temperature of not more than 720° C., to fill the third claddinglayer inside the extension in such a manner that a surface of the thirdcladding layer is flush with the surface of the current constrictivelayer; and successively growing a first cladding layer, an active layer,and a second cladding layer over the substrate to form a doubleheterostructure.
 4. A method of making a semiconductor light-emittingdevice comprising the steps of:forming on a surface of a GaAs substratehaving one of p- and n-conductivity types a current constrictive layercomprised of GaAs or AlGaAs and having the other of the p- andn-conductivity types, the surface being (111)B face or a face offset tothe (111)B face which is a main face; forming in the currentconstrictive layer a plurality of through-channels of a predeterminedpattern which extend from a surface of the current constrictive layer tothe substrate; growing third cladding layers comprised of AlGaAs andhaving the one type of conductivity within the respectivethrough-channels while the substrate is kept at a temperature of notmore than 720° C., in such a manner that a surface of each of the thirdcladding layers is flush with the surface of the current constrictivelayer, thereby filling the through-channels; and successively growing afirst cladding layer, an active layer, and a second cladding layer overthe substrate to form a double heterostructure.
 5. A method of making asemiconductor light-emitting device comprising the steps of:forming on asurface of a GaAs substrate having one of p- and n-conductivity types acurrent constrictive layer comprised of GaAs or AlGaAs and having theother of the p- and n-conductivity types, the surface being (111)B faceor a face offset to the (111)B face which is a main face; forming in thecurrent constrictive layer a non-through channel of a predeterminedpattern which is held within the current constrictive layer; forming inthe current constrictive layer a through-channel of a predeterminedpattern which extends from a surface of the current constrictive layerto the substrate; growing third and fourth cladding layers comprised ofAlGaAs and having the one type of conductivity respectively within thethrough-channel and non-through channel while the substrate is kept at atemperature of not more than 720° C., to respectively fill thethrough-channel and non-through channel with the third and fourthcladding layers in such a manner that the surfaces of the third andfourth cladding layers are respectively flush with the surface of thecurrent constrictive layer; and successively growing a first claddinglayer, an active layer, and a second cladding layer over the substrateto form a double heterostructure.
 6. A method of making a semiconductorlight-emitting device comprising the steps of:forming on a surface of aGaAs substrate having one of p- and n-conductivity types a currentconstrictive layer comprised of GaAs or AlGaAs and having the other ofthe p- and n-conductivity types, the surface having (111)B face or aface offset to the (111)B face which is a main face; forming in thecurrent constrictive layer a through-channel of a circular pattern whichextends from a surface of the current constrictive layer to thesubstrate; growing a third cladding layer comprised of AlGaAs and havingthe one type of conductivity within the through-channel while thesubstrate is kept at a temperature of not more than 720° C., to fill thethrough-channel with the third cladding layer in such a manner that asurface of the third cladding layer is flush with the surface of thecurrent constrictive layer; successively growing a first cladding layer,an active layer, and a second cladding layer over the substrate to forma double heterostructure; and working the layer forming the doubleheterostructure to a frusto-conical configuration.